Investigation of the wild horse deaths in the Orr springs area of Dugway Proving Ground led to the following information: The weather had been exceptionally hot and dry prior to, and during, the incident. The water hole at Orr Springs used by the horses had been modified by the Bureau of Land Management in an effort to provide improved water supply. The new water supply eliminated the customary water source. Low stakes with flags surrounded the new supply; in close proximity to the new supply were two large piles of creosoted poles which emitted a strong odor. There was no evidence of use by horses of a newly installed watering trough. None of the chemical and microbiological examinations of soil suggested properties causing the demise of the horses. On-site inspection of plants showing evidence of having been grazed upon as well as examination of gastrointestinal contents verified that the horses had not consumed a significant amount of toxid plants. Potential disease vectors were evidently not involved in the horse incident. The rodent population in the Orr Springs area had not suffered from a similar catastrophe. Microbiological tests failed to provide evidence for an infectious disease. Speculations were made that the horses were poisoned by Compound 1080, sodium fluoroacetate. This highly toxic substance was banned a number of years ago. It was concluded that the wild horses died as a result of dehydration.